In lighting assemblies used in automotive applications, for example, a particular requirement is that the bright/dark “cut-off” line of the light output by the lighting assembly satisfies certain regulations. Furthermore, this bright/dark cut-off line should be adaptable. The overall beam of light output by the lighting assembly should be adjustable, for example, to produce a low beam for illuminating the region directly in front of the vehicle and a high beam for extending the illuminated area. Adaptability of the light output is also desirable in certain situations, such as when driving into a bend, so that the area in the bend can be better illuminated with a resulting increase in safety. Furthermore, it may be advantageous to influence the amount of light in the foreground of the beam pattern, i.e. in a region of the beam closest to the vehicle, depending on traffic conditions and/or terrain, weather conditions, etc.
The high beam and low beam have conventionally been generated using separate light sources in two separate lighting arrangements. Using conventional filament lamps or gas-discharge lamps, generally two lighting units are mounted in close proximity in a headlamp arrangement and configured so that the high beam and low beam are projected correctly into the relevant regions in front of the vehicle. Although headlamp optical systems do not use true “imaging” optics, usually one edge of the source or an edge of a shield element is “imaged” in order to obtain the required cut-off for the beam distribution. The quality of the light beams must satisfy certain requirements. For example, the shapes or contours of the light beams that would be projected onto a vertical transverse plane located at a standard distance from the headlamp, e.g. 25 meters, are covered by national and international specifications such as ECE (Economic Commission for Europe) R112.
Lighting units or lighting assemblies using semiconductor light sources such as light-emitting diode (LED) chips are becoming more popular as advances in technology have led to economic and yet very bright semiconductor light sources. Since semiconductor light sources are compact, it would be convenient to combine two such light sources for two different beam functions into a single arrangement. However, known solutions have not shown satisfactory results. Because the light from each light source is directed at the single optical element, the physical separation between the two sources is also imaged and appears as a ‘gap’ between the projected beams, for example as a dark area between a low beam and a high beam. Even a minimal gap between the light source images results in a visual gap in the beam distribution. This can be a safety hazard when driving, since anything in this region is effectively invisible to the driver. In particular the verge or curb region to the side of the vehicle is critical, since pedestrians, animals or hazards in this region are then effectively invisible to the driver. Furthermore, because the secondary optic is ‘shared’, it must of necessity be larger, and the overall arrangement is about as large as an arrangement having separate optical systems for each function, so that the advantage of a compact light source is lost. The optical element could be designed to distort the beams in order to close this gap, but such a distortion unavoidably has a detrimental effect on the bright/dark cut-off line, which may then no longer satisfy the requirements. Furthermore, any corrective measures of the optical element affect both beams, so that a controlled correction of separate beams is not feasible.
Therefore, it is an object of the invention to provide an improved lighting arrangement that avoids the problems mentioned above.